Reptiles

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Reptiles
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Reptiles

• First truly terrestrial vertebrates
• 7000 species worldwide
• 300 species in U.S. and Canada

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Reptiles

• Probably best remembered for what they once were,
  rather than what they are now
• Mesozoic era - age of reptiles
• Dominant group for gt150 millions years

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Reptiles

• 12 or so principal groups of reptiles evolved
• Only 4 groups remain today

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Order Squamata

• Snakes and lizards
• gt5800 species
• Most successful group

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Order Crocodilia

• Crocodiles, alligators, caiman
• 25 species
• Have survived for 200 million years
• Today concerns that humans may drive them to
  extinction

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Order Chelonia (Testudines)

• Turtles
• 330 species
• Ancient group that survived, remained mostly
  unchanged from early ancestors

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Order Rhynchocephalia

• Snout head or tuatara
• Only 1 species
• From New Zealand - sole surviving species of
  ancestral stock

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Reptilian Characteristics

• Tough, dry scaly skin
• Protection against desiccation, physical injury
• Thin epidermis shed periodically
• Much thicker dermis with chromatophores

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Reptilian Characteristics

• Dermis converted into snakeskin, alligator
  leather for shoes, purses, and so on
• Scales of keratin (epidermal)
• Not homologous to bony, dermal fish scales

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Reptilian Characteristics

• Crocodilian scales remain throughout life
• Grow gradually to replace wear

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Reptilian Characteristics

• In snakes and lizards, new scales grow beneath
  old
• Old scales shed with old skin

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Reptilian Characteristics

• Turtles add new layers of keratin under old
  layers of the plate-like scutes (modified scales)

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Shedding

• Snakes turn old skin (scales, epidermis) inside
  out when shedding

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Shedding

• Lizards split skin and leave it right side out,
  or slough it off in pieces

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Amniotic Egg
Chorioallantoic membrane
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Amniotic Egg

• Reptiles are able to lay their eggs in sheltered
  locations on land
• Young hatch as lung-breathing juveniles, not
  aquatic larvae

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Amniotic Egg

• Amniotic egg widened division between amphibians
  and reptiles
• Probably greatly contributed to decline of
  amphibians and rise of reptiles

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Reptile Jaws

• Reptile jaws designed for crushing prey
• Fish, amphibian jaws designed for quick closure,
  but little force after
• Reptile jaw muscles larger, longer, arranged for
  better mechanical advantage

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Reptile Copulatory Organ

• Copulatory organ permitting internal
  fertilization
• Internal fertilization required for a shelled egg
• Copulatory organ formed from an evagination of
  cloaca

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Reptile Circulation

• More efficient circulatory system, higher blood
  pressure
• All reptiles have at least an incomplete
  separation of the ventricles
• Flow patterns prevent mixing

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Reptile Circulation

• Crocodilians have two completely separated
  ventricles
• All reptiles have two functionally separate
  circulations

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Reptile Lungs

• Improved lungs
• Depend almost exclusively on lungs for gas
  exchange
• Supplemented by pharyngeal membrane respiration
  in some aquatic turtles

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Reptile Lungs

• Lungs have larger respiratory surface than in
  amphibians
• Air sucked into lungs rather then forced in by
  mouth muscles
• Negative pressure
• Skin breathing completely abandoned

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Reptile Kidney

• Kidneys more advanced (metanephric)
• Very efficient at conserving water
• Excretes uric acid (rather than urea, ammonia)
• A semisolid paste

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Better Body Support

• Limbs better design for walking on land
• More ventral, less lateral
• Many dinosaurs walked on only hindlimbs

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Nervous System

• Much more advanced - relatively larger cerebrum
• CNS connections more advanced - permit complex
  behaviors not found in amphibians

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Nervous System

• Sense organs generally well-developed
• Hearing generally poorly developed in most

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Order Chelonia

• Turtles
• Very ancient group
• Little change in morphology since Triassic period

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Order Chelonia

• Body enclosed in shell
• Dorsal carapace
• Ventral plastron

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Order Chelonia

• Thoracic vertebrae and ribs built into shell
• Shell of two layers
• Inner of bone
• Outer of keratin
• New keratin deposited under old as turtle grows,
  ages

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Order Chelonia

• Jaws lack teeth
• Equipped with tough, horny plates for gripping,
  chewing food

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Order Chelonia

• Respiration poses a problem
• Shell prevents expansion of chest for breathing
• Adapted to use certain abdominal, pectoral
  muscles as a diaphragm

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Order Chelonia

• Air drawn in by contracting limb flank muscles to
  make body cavity larger
• Exhalation also active - shoulder muscles
  contracted, viscera compressed, air forced out of
  lungs

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Order Chelonia

• Deformable plastron in snappers allows some
  elastic recovery during exhalation
• Compressive force of water against body also can
  force air out

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Order Chelonia

• Many water turtles acquire enough O2 when
  inactive by pumping water in and out of mouth
• Pharyngeal breathing
• Can stay submerged for extended periods
• Must lung breathe more frequently when active

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Order Chelonia

• Nervous system - tiny brain
• Typical of most reptiles
• Never exceeding 1 of body weight, but cerebrum
  larger than in amphibians
• Turtle can learn, as quickly as a rat, to run a
  maze

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Order Chelonia

• Have both middle inner ear, but sound
  perception is poor
• Turtles are virtually mute
• Tortoises may grunt or roar

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Order Chelonia

• Poor hearing compensated for by
• Good sense of smell
• Acute vision
• Color perception as good as that of humans

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Order Chelonia

• Mating reproduction
• Many varieties of courtship
• Males of aquatic species may swim around looking
  for proper leg stripe pattern
• Pheromones also
• Males use claws

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Order Chelonia

• Terrestrial species may vocalize
• Males may track females (pheromones) for days

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Order Chelonia

• Males may mark territory with fecal pellets
• Courtship involves rubbing limbs against scent
  glands (underside of jaw) and sniffing

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Order Chelonia

• Biting, ramming, hooking are directed at other
  males
• Biting - head limbs
• Ramming - rearing up, smacking shells
• Hooking - bulldozing under plastron to flip or
  hurry

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Order Chelonia

• Turtles are oviparous
• Fertilization is internal, and all species bury
  eggs in ground in nests
• 4 to gt100 eggs

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Order Chelonia

• Exercise care in constructing nest
• Deposit eggs and abandon them
• Incubation 1-14 months
• 40-60 days most typical

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Order Chelonia

• Movements to nesting areas very faithful
• Terrestrial species use familiarity with area,
  sun
• Marine species use variety of mechanisms to
  traverse large distances

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Order Chelonia

• Earths magnetic field
• Polarized light
• Sun stars
• Low frequency sounds
• Green sea turtles find Ascension Island (20 km)
  in mid-Atlantic from coastal Brazil - 2200 km

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Order Chelonia

• Size - marine turtles largest
• Buoyed by aquatic environment
• May reach 2 m in length, 725 kg in weight
• Biggest species is leatherback

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Order Chelonia

• Green sea turtle may exceed 360 kg
• Economically valuable - heavily exploited -
  rarely gets to large size

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Order Chelonia

• Land tortoises generally not as large as aquatic
  forms
• Some may weigh several hundred kg
• Giant tortoises of Galapagos Islands among
  worlds largest terrestrial turtles

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Order Chelonia

• Lifespan - turtles are most long-lived
  vertebrates
• Individuals of at least 5 species known to live
  100 years or longer
• Some believed to have lived more than 150 years

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Order Chelonia

• Longevity attributed to slow rate of metabolism
• Galapagos tortoise top speed 300 m/hr
• Reports of box turtle caught in U.S. with 1850
  carved into plastron
• Skepticism!

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Order Chelonia

• Protective shell
• Head, appendages can be drawn in for protection
• Box turtles especially good because of hinged
  plastron

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Order Chelonia

• Shell not as protective in many species
• Soft, leather-like in softshell turtles

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Order Chelonia

• Shell too small for protection in other species,
  e.g., snappers
• Other means of defense - ferocious,
  short-tempered
• Tigers of the pond

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Order Chelonia

• Entirely carnivorous - fish, frogs, ducks,
  whatever they can catch
• Alligator snapper hides on bottom and waves
  worm-like tongue to attract fish
• Wholly aquatic - come ashore only to lay eggs

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Turtle Conservation

• Slow growth, long time to maturity predispose
  many species to risk of extinction
• Changing conditions may increase adult mortality,
  juvenile recruitment

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Turtle Conservation

• Problem severe for large tortoises, sea turtles
• Largest, slowest-growing
• Human and animal invasion of beaches, isolated
  island habitats

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Turtle Conservation

• Herbivores compete with tortoises for limited
  vegetation
• Eggs, young fall prey to dogs, cats, rats

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Turtle Conservation

• Protection of land tortoises simpler than
  protection of sea turtles
• Limited range (single island) defines limits
  where protection is needed

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Turtle Conservation

• Sea turtles range over international, national
  borders
• Limited number of breeding sites
• Problems with exploitation - controlled or
  outright ban?

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Turtle Conservation

• Ocean plastics pollution - bags look like natural
  jellyfish prey
• Not enough known about biology do devise
  protective management program
• Tag a turtle? 2000 X

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Order Squamata

• characterized by scales
• Lizards, snakes, worm lizards
• Most recent products of reptile evolution
• Most successful - 95 of known living species of
  reptiles

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Order Squamata

• Lizards began diversifying at time when dinosaurs
  were near end of their dominance
• Were successful because of adaptability
• Adopt various body forms, occupy various habitats

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Order Squamata

• Snakes likely arose from group of lizards whose
  descendents include monitor lizards, but fossil
  record poor

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Order Squamata

• Legless character apparently evolved as
  adaptation to burrowing lifestyle
• Snakes since have radiated into terrestrial,
  aquatic, arboreal niches

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Order Squamata

• Two adaptations characterize snakes
• Extreme body elongation - displacement,
  rearrangement of organs
• Highly mobile jaws - swallow prey larger than own
  diameter

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Order Squamata

• Two suborders
• Sauria - lizards
• lizard
• Serpentes - snakes
• to creep

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Lizards

• Very diversified group (3300 species)
• Terrestrial, burrowing, aquatic, arboreal, aerial
• Many familiar groups

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Lizards

• Geckos
• Mostly small, nocturnal, with adhesive toe pads
  (walk anywhere)

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Lizards

• Iguanas
• Often bright-colored New World lizards
• Marine iguana - only marine lizard in world

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Lizards

• Skinks
• Elongate bodies, reduced limbs

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Lizards

• Chameleons
• Arboreal
• Tongue flicked to greater distance than body
  length
• Prehensile tail
• Zygodactylous feet

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Lizards

• Independently moveable eyes elevated on cones -
  good eyesight - gauge distance accurately

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Lizards

• Lizard body form not as distinctive as other
  reptiles
• Many functional, behavioral modifications
• e.g., degenerate or absent limbs - no good in
  dense grass

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Lizards

• Differ from snakes
• Halves of lower jaw firmly united at mandibular
  symphysis
• Teeth, but not developed into fangs

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Lizards

• Moveable eyelids (snake eyes covered with
  permanent, transparent cap)
• Keen daylight vision

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Lizards

• Size - 3 cm to 3 m
• Hawaiian gecko
• Komodo dragon
• 75 kg
• Fossils 5.5 m, gt1000 kg

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Lizards

• 80 of lizards are lt20 g in weight
• Generally insectivorous (opportunistic), although
  some specialists
• N. Amer. horned lizards eat only ants

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Lizards

• Most large lizards are herbivores
• Trees in tropics, ground vegetation on oceanic
  islands, seaweed in ocean

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Lizards

• Monitor lizards are exception to vegetarians
• Food of vertebrates (birds, mammals),
  invertebrates
• Komodo - ambush predator on large mammals (deer,
  goats, water buffalo)

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Lizards

• Foraging strategies
• Sit and wait (insects come to them)
• Active foragers (move to encounter prey)

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Lizards

• Foraging modes alternate at successive levels of
  food chain
• Moving insect -gt sit-and-wait lizard -gt active
  predator
• Sitting insect -gt active lizard -gt sit-and-wait
  predator

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Lizards

• May use territorial and courtship behaviors
• Male anoles have gular fan (dewlap) for
  conspicuous displays
• Skin distended by hyoid apparatus

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Lizards

• Behaviors include
• Extending, contracting fan
• Pushups
• Bobbing head

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Lizards

• Territories defended by males for access to
  females (bite chase, but no fighting)
• Females have non-overlapping home ranges for
  feeding
• Male territory includes several females - mates
  with all

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Lizards

• Mate by pressing cloacal regions together
• Males grip females neck, shoulders
• Males have paired copulatory organs - hemipenes -
  to aid sperm transfer

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Lizards

• Range of reproductive modes from oviparity to
  viviparity
• Skinks - eggs retained in oviducts, receive
  nutrients across a placenta

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Lizards

• All-female (parthenogenetic) species occur in at
  least 6 families
• Especially common among racerunners (Teiidae)
• Diploids and triploids known

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Lizards

• High reproductive potential - every individual
  capable of producing offspring
• Can repopulate habitat faster than bisexual
  species after flood, other disaster

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Lizards

• Parental care
• Many lizards remain with eggs or nest site
• Little if any care given after young hatch or are
  born

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Suborder Serpentes - Snakes

• 2300 species
• 10 cm long up to 10 m long
• Highly specialized body form

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Suborder Serpentes - Snakes

• Entirely limbless
• Lack pectoral, pelvic girdles (except vestige of
  latter in pythons, boas)
• Short, wide vertebrae for quick lateral
  undulations
• Ribs improve rigidity

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Suborder Serpentes - Snakes

• Rearranged internal anatomy
• Left lung reduced or absent
• Gall bladder posterior to liver
• Right kidney anterior to left
• Gonads similarly displaced

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Suborder Serpentes - Snakes

• Little modification for various lifestyles
• Elongate for arboreal
• Shorten for burrowing
• Broaden for swallowing big prey
• Compress laterally for swimming

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Snake Sense Organs

• Snake, lizard eyes different focusing, retina
  morphology
• Re-evolved from burrowing ancestors
• Permanent transparent covering - non-blinking
  stare
• Lack of eyeball mobility
• Poor vision - except binocular in arboreal snakes

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Snake Sense Organs

• Hearing - no obvious external ear
• No obvious response to aerial sounds
• Not deaf - have internal ears - hearing similar
  to lizards
• Sensitive to vibrations carried in ground

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Snake Sense Organs

• Olfaction important, but not in nostrils
• Jacobsons organs (vomeronasal organs)
• Tongue carries scent particles to organ

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Snake Feeding

• Skull, jaws highly specialized for feeding
• Eat prey several times their own diameter
• Non-joined mandibles
• Loose skull bones
• Tracheal opening far forward between mandibles

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Snake Feeding

• Prey swallowed head first
• Pulled in by teeth, jaws, alternating
  side-to-side
• Contractions of neck muscles force prey down
  digestive tract

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Snake Feeding

• Two ways to subdue prey
• Constricting - grab prey in mouth and suffocate
  by looping body coils and tightening

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Snake Feeding

• Venom - toxic concentrations in saliva
• Neurotoxic - blindness, paralysis
• Hemolytic - ruptures blood vessels, cells

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Snake Feeding

• Poisonous snakes in 4 families
• Viperidae - viper, pit vipers (heat sensitive)
• Elapidae - coral snakes (inject venom by chewing)
• Hydrophiidae - sea snakes
• Colubridae - rear-fanged - venom to calm, not kill

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Snake Feeding

• Sea snakes have most deadly venom
• King cobra most dangerous, largest (5.5 m) - kill
  9,000 people per year

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Snake Locomotion

• 4 basic types
• Lateral undulation - S-shaped path, pressure
  against surface irregularities

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Snake Locomotion

• Concertina movement - movement upward or along
  narrow passages
• Extend forward while bracing S-shaped loops

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Snake Locomotion

• Rectilinear movement - slow, straight-line
  movement

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Snake Locomotion

• Sidewinding - sandy surfaces, body thrown forward
  in loops, body at 60 angle to line of travel, 1
  or 2 parts of body in contact with ground at once

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Snake Reproduction

• Most oviparous - lay eggs in protected areas
• Most of remainder are ovoviviparous (including
  rattlesnakes)
• Very few viviparous
• Females store sperm from single mating, can lay
  several clutches over long interval

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Order Crocodilia

• Unchanged for 160 million years
• Crocodiles larger, more dangerous than alligators
• Prey drowned, ripped into pieces by rapid rolling
• No natural enemies

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Order Crocodilia

• Oviparous - lay eggs in mass of vegetation
• Guarded by mother
• Incubation temperature determines sex of
  alligator hatchlings
• Low - females
• High - males
• 51 (MF) in some areas

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Order Crocodilia

• Vocalizations by hatchlings cause mother to open
  next, allow hatchlings to escape
• Some adults carry young to water

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Order Crocodilia

• Mothers may guard young in pools for period of
  time to protect them from predators (fish,
  mammals)

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Order Sphenodonta

• Tuatara - single species in New Zealand
• Lizard-like, lt66 cm
• Lives in burrows
• Slow-growing, long-lived (77 years)

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Order Sphenodonta

• Living fossil - primitive features identical to
  fossilized forms
• Primitive skull structure
• Well-developed parietal eye with retina, lens on
  top of head (non-functional)